This proposal is directed toward an understanding of the role of repetitive DNA sequences in gene expression. The slime mold Dictyostelium discoideum will be used as a test organism; the program will focus primarily on these points and in that order of priority: 1) Characterization of Hn-RNA-associated reiterated DNA transcripts isolated from amoebae at various stages of growth and development. State-specific sequences should be detected, if these transcripts serve a role in transcriptional control during cell differentiation. 2. Correlation of posttranscriptional modifications ('CAP' formation, poly A formation, drain cleavage, methylation) with specific classes of reiterated DNA transcripts associated with either HnRNAs or cytoplasmic mRNAs. 3. Reconstitution of an in vitro RNA processing system in a search for stage-specific maturation factors which may effect gene expression at the level of RNA processing. 4) Characterization of reiterated DNA transcripts in polysome-associated and in free cytoplasmic mRNAs isolated from different stages of development and growth. 5) Isolation and characterization of genes which code for tRNAs.